Have you ever come across the factoid that cars only get used 5% of the time you have them. In other words, 95% of the time your car is parked doing nothing. Seems a little exaggerated doesn't it? And who exactly came up with this number?

As it turns out, several firms have calculated this number and they all do it differently. For those that enjoy a little math with your car articles, here's the story.

Method #1

Method #1 comes from the Royal Automobile Club (RAC). The RAC has a foundation that conducts research to assist those that develop transport policy. Their research explores the economic, mobility, safety and environmental issues relating to cars and roads.

Here's the math: They start with the fact that in the UK there are about 25 billion car trips per year taken by some 27 million cars. This suggests an average of about 18 trips per car per week. In another study they determined that the duration of the average car trip is about 20 minutes, therefore the typical car is only on the move for 6 hours in the week. Since there are 168 hours in a week, the typical UK car is parked 96.5% of the time.

Method #2

We learned about Method #2 from Leckner Ford of King George, VA. Their data comes from Nationwide Personal Transportation Survey (NPTS) of the US Department of Transportation. The NPTS determined that the average time drivers spent driving was 73 minutes per day. Assuming one car per driver (which is roughly OK for the US context), this gives 5.1% as the time each car is in motion. This translates to being parked for 94.9% of the time.

Method #3

Transportation studies for metropolitan areas often provide data on the average yearly distance driven per car and the overall traffic speed. These are important statistics for urban planners. So, you can use this easy method to determine the utilization rate of automobiles. You divide total car km by the number of cars, being careful that the two numbers are for the same study area. The average time each car is in motion is the car km per year divided by the average speed. Using this method, the average percentage of time that cars were parked for the 84 cities in that study was 95.8%. They were typically being driven for 1.02 hours per day.

Why should I care?

One reason to calculate this is to simply get data on car usage. After all, it appears that parking is what cars do the vast majority of the time. For policy types, it highlights the inefficiency of private car ownership. For urban planners, it allows them to design urban traffic flow easier.

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